Abstract Submission - Chun YANG - Laboratoire de Physico-Chimie de l’Atmosphère
Monitoring of gas phase pollutant by continuous-wave terahertz spectroscopy.
Various spectral lines, such as pure rotational transitions of small polar atmospheric pollutants and lowfrequency vibration transitions of large organic molecules, are expected to lie in the terahertz region. A continuous-wave spectrometer based on a photomixing source has been constructed with two tunable diode lasers providing access to the frequency region from 0.3 THz to 3.3 THz with a spectral purity of 0.5 MHz at - 3dB. This spectral coverage allowed us to determine air-broadening coefficients of hydrogen cyanide (HCN), which have been included in the HITRAN database to serve as reference parameters for planetary and atmospheric analysis (earth, Titan...). The detection limit for HCN was estimated to be 2.4 ppm/m.
To increase the spectrometer sensitivity a multipass cell has been used to extend the optical path. Molecular transitions with an intensity as weak as 10-25 cm-1/(molecule.cm-2) have been observed for the measurements of carbonyl sulfide isotopes O13CS in terahertz region. The increased sensitivity allowed preliminary measurements of volatile organic compounds (VOC), dimethyl sulfoxide ((CH3)2SO) and vinyl chloride (CH2CHCl), to be performed. Many rotational transitions are required to refine the molecular constants which can in turn be used for molecular identifications over a large spectral range. The quantitative analysis of cigarette by this technique will also be presented.
